John Calvin Commentary Acts 13:39

"and by him every one that believeth is justified from all things, from which ye could not be justified by the law of Moses." — Acts 13:39 (ASV)

Every one that believeth. Paul shows how people obtain the righteousness of Christ: namely, when they receive it by faith. And what faith obtains is not obtained by any merits of works. Therefore, Paul’s opinion is plain: we are justified by faith alone. Although the Papists oppose and strive against this no less obstinately than bitterly, it is nevertheless essential that we know what the word believe means, which is made unpalatable to the Papists through ignorance.

There are also other benefits of Christ that we reap by faith. For when He regenerates us by His Spirit, He restores in us the image of God; and after the old man is crucified, He fashions us to newness of life. But it was enough for Luke to express this one thing: how people return to favor with God, from whom they are estranged by sin, because we may easily pass from there to the rest.